The predominant trend in the disk drive industry for the past several years has been to increase track density in order to achieve increased data storage capacity. One of the difficulties which must be overcome in achieving this goal, however, is the ability to maintain tracking position accuracy as the track density increases.
A major source of tracking position inaccuracy in computer disk drive systems is spindle bearing motion--commonly referred to as "runout". Conventional drives utilize ball bearing assemblies which are prone to numerous mechanical problems, such as large runout, wear, complex manufacturing requirements, and so on. In an attempt to overcome these problems and attain higher track densities, many companies in the disk drive industry are focusing their attention on alternative spindle bearing designs.
As an alternative to conventional ball bearing spindle systems, researchers have concentrated much of their efforts on developing a hydrodynamic bearing. In these types of systems, a lubricating fluid--either air or liquid--functions as the actual bearing surface between a stationary base or housing and the rotating spindle or rotating hub and stationary spindle. For, example, liquid lubricants comprising oil or more complex ferromagnetic fluids have been developed for use in hydrodynamic bearing systems.
In the case of a hydrodynamic bearing employing a liquid lubricant, the lubricating fluid itself must be sealed within the bearing. Otherwise, the physical surfaces of the spindle and housing would contact one another leading to increased wear and eventual failure of the bearing system. Most often, these seals are accomplished by developing a pressurized film on the surface of the liquid/air interface. In the case of bearing assemblies which employ ferromagnetic fluids, the seal is achieved by means of a magnetic field established at each end of the bearing. By way of example, a radial bearing assembly which utilizes a ferromagnetic fluid is disclosed in U.S. Pat. No. 4,526,484. Hydrodynamic bearing assemblies in which oil acts as the lubricating fluid are disclosed in U.S. Pat. Nos. 5,067,528 and 4,795,275.
In the past, hydrodynamic bearing assemblies have suffered from numerous disadvantages. For example, bearing assemblies which utilize ferro fluids are known to suffer leakage problems as metallic particles suspended within the ferro-fluid solution are gradually pulled out over time. Obviously, any leakage of the lubricating fluid within the disk drive assembly can cause considerable performance problems.
Other shortcomings include the fact that many prior art hydrodynamic bearing assemblies frequently require large, bulky structural elements for supporting the axial and radial loads. Such assemblies are not generally scaleable to the smaller drive dimensions currently in consumer demand. In other instances, prior hydrodynamic bearing assemblies suffer from the disadvantage of requiring extremely tight clearances and alignments. This burden often makes it difficult to manufacture such assemblies since even a small deviation or aberration in a component's dimension or alignment tolerance can lead to a faulty bearing. As an example, misalignment of the spindle relative to the housing or base during the assemblage of the disk drive can create lateral deflection forces which act upon the bearing. These forces cause uneven pressures to develop, eventually resulting in increased wear of the bearing components.
As will be seen, the present invention provides an extremely simple and highly scaleable hydrodynamic bearing assembly for use within an information storage unit such as a computer disk drive system. The invention overcomes the shortcomings of the prior art and is characterized by its scaleability, ease of assembly, and support of axial and radial loads with a minimum number of components. The invention further includes a means for adjusting the bearing clearance in a precise and controlled manner.
Other prior art known to Applicant includes a thesis paper by J. P. Reinhoudt entitled, "On the Stability of Rotor-and-Bearing Systems And On The Calculation of Sliding Bearings," dated February 1972.